1. Field of the Invention
The present invention relates to the field of guiding bearings for a turbine engine shaft and, more precisely, a fluidic dampening film supply method for a guiding bearing.
2. Description of the Related Art
The guiding bearings being used in a turbine engine include an internal ring and an external ring enclosing rolling members, for example rolls. Conventionally, the external ring is integrally mounted on a fixed part of the turbine engine and the internal ring is integrally mounted on a turbine engine shaft, for example by shrunk-fitting. The bearing thus allows the rotating shaft to be guided relative to the fixed part of the turbine engine.
In some configurations, the bearing is mounted between two rotating shaft of the turbine engine. Such a bearing is currently called “inter-shaft” bearing, such a bearing being for example known from the patent application FR 2,939,843 A1 from SNECMA Company.
As an example, referring to FIG. 1, a turbo-jet for an aircraft conventionally comprises several rotating turbine shafts, a high pressure shaft HP of which is rotationally mounted relative to a low pressure shaft BP via an inter-shaft guiding bearing 1. The guiding bearing 1 comprises an external ring 11 being integral with a part of the low pressure shaft BP and an internal ring 12 being integral with a part of the high pressure shaft HP and rolling means 13 enclosed by the ring 11, 12. In this example, the internal ring 11 is shrunk-fitted on the high pressure shaft HP so as to prevent any translation and any rotation of the internal ring 12 of the bearing 1 relative to the high pressure shaft HP. In order to dampen the movements of the shafts BP, HP, the guiding bearing 1 comprises a fluidic dampening film 14 captured between the external ring of the bearing 1 and the rolling means 13 of the bearing 1 thanks to seals, not shown.
A fluidic dampening film 14 of a guiding bearing 1, being known from the man of the art under the designation “squeeze-film” allows the dynamical response of the turbine engine to be improved at a given operation speed. Preferably, the fluidic dampening film comprises oil under pressure. It enables for example to limit the vibrations of the turbine engine during the operation thereof. Conventionally, the turbine engine comprises a main supplying pump 2 being adapted to supply the fluidic dampening film 14 at a supplying pressure Pp which is a function of the turbine engine speed. Thus, the supplying pressure of the fluidic dampening film 14 is higher at high speed (take-off phase of the aircraft) than at low speed. In practice, the supplying pressure of the dampening film is not sufficient at low speed and dampening is not optimal.
In order to obtain the desired dampening and avoid the cavitation of the oil film in the guiding bearing, it is known to increase the oil supplying pressure of the fluidic dampening film 14 with the help of an additional supplying pump 3 being known from the man of the art under the designation “boost-pump”. At low speed, the additional supplying pump advantageously allows an additional pressure Pa to be supplied in order to compensate for a defect of the supplying pressure Pp of the main supplying pump 2 so that the fluidic dampening film 14 is supplied at the increased supplying pressure.
In practice, the additional supplying pump 3 is activated at low speed so as to increase the supplying pressure up to a target pressure enabling to bring some dampening to the turbine engine. When the rotation speed of the turbine engine is sufficient to allow the main supplying pump 2 to supply the appropriate supplying pressure, the additional supplying pump 3 is inactivated.
It has been observed that, in spite of a supply of the dampening film at the optimum supplying pressure thereof over its speed range, the amplitudes of the vibrations in the turbine engine are not optimally reduced.